Ultra high frequency attenuator



Sept. 10, 1946. E. L. GINZTON I ULTRA HIGH FREQUENCY ATTENUATOR FiledMarch 5 1943 2 Sheets-Sheet 1 INVENTOR EDWARD L. GINZTQN BY W/AM'ATTORNEY Sept. 10; 1946. E, GINZTQN 2,407,267

ULTRA HIGH FREQUENCY ATTENUATOR Filed March 5, 1945 2 Sheets-Sheet 2INVENTOR EDWARD L. GINZTON ATTORNEY Patented Sept. 10, 1946 UNITEDSTATES PATENT OFFICE ULTRA HIGH FREQUENCY ATTEN'UATOR Edward L. Ginzton,Wantagh, N. Y., assignor to Sperry Gyroscope Company, Inc., Brooklyn, N.Y., a corporation of New York Application March 5, 1943, Serial No.478,163

' 13 Claims. 1

The present invention relates to devices for attenuating ultra highfrequency electromagnetic energy, and especially to devices adapted foruse in concentric transmission line systems or in wave guide systems.

In many high frequency systems it is necessary or desirable to attenuatethe energy derived from an ultra high frequency source or flowing in ahigh frequency circuit by a predetermined amount. In prior copendingapplication Serial No. 452;:319, filed July 25, 1942, in the name of W.W. Hansen, there are disclosed a number of types of attenuators suitablefor use with concentric transmission lines or wave guides. Suchattenuating devices, provided with means for preventing undesired wavereflections or standing waves, are variable over considerable range andare of fixed length whereby they may be perinanently and rigidlyconnected in the system wherein they are used.

The present invention constitutes an improvement over the attenuatorsshown in the prior copending application. In this prior application, theseveral forms of attenuator shown utilize adjustable lengths of waveguide having crosssectional dimensions smaller than the minimum requiredfor free propagation of the ultra high frequency energy which may betermed the cut-off dimension. As is therein described, such cut-ofi waveguides serve to attenuate the energy supplied to them, the amount ofattenuation being related to the length of the wave guide section.However, the attenuators of the prior application have required specialapparatu for coupling either a concentric transmission line or a waveguide to the attenuator wave guide section in order to provide thedesired attenuation, Furthermore, the required adjustability of thedevices of the prior application was obtained only by the use of varioussliding or telescoping joints which rendered these devices relativelycomplicated and diflicult to manufacture.

By the present invention, I provide several types of adjustableattenuator utilizing the same principle of a wave guide dimensionedbelow cutoff, but providing ease of adjustment and construction andeliminating the necessity for special coupling or metallic telescopingjoints or sliding joints.

Accordingly, it is an object of the present invention to provideimproved ultra high frequency attenuating device which are relativelysimple to adjust and construct.

It is a further object of the present invention to provide improvedattenuating devices which may be directl connected to concentric line orwave guide utilization devices or energy sources.

It is still another object of the present inven v tion of a modificationof the attenuator of Fig. 1.

Fig. 4 shows a cross-section of the device of Fig. 3 taken along line 44thereof.

Fig. 5 shows a perspective view of another modification of the presentinvention.

Fig. 6 shows a transverse cross-section of the device of Fig, 5 takenalong line 6-5.

Fig. '7 shows another transverse cross-section of the device of Fig. 5'taken along line 1'|.

Fig. 8 shows a longitudinal horizontal crosssection of still anotherform of the present invention.

Fig. 9 shows a transverse cross-section of the device of Fig. 8 takenalong line 9-9 thereof.

Referring to Figs. 1 and 2, the wave guide attenuator according to thepresent invention is supported on a stand I I by means of posts I! and[3 in which are clamped wave guides II and I6, either of which may bethe input terminal to or the output terminal from the attenuator ofFig. 1. Although wave guides H and is are indicated as rectangular inform, it is to be understood that this showing is purely illustrativeand that other shapes and forms of wave guides,.s'uch as, circular,elliptical, and otherwise, may be utilized. Preferably the main body ofthe attenuator oi the invention is formed of a cylindrical casing l1Whose diameter is so chosen that, at the operating frequency of thedevice, cylinder II, when acting as a wave guide, would have dimensionsbelow cut-off when filled solely with air.

If we'consider for the moment that wave guide It represents the energyinput to the attenuator, it will be seen that this energy is then ledtocylinder ll through the T-connection of wave guide l4 and cylinder ll.At the junction of wave guide It and cylinder I1 is placed a block orplug ll of dielectric material. This plug H! made axially adjustablewith respect to cylinder II, by means of a slot l8 formed in cylinder l1which cooperates with a set screw 2I passing through a ring 20 slidableon the outside of cylinder l1. By loosening screw 2|, plug I8 may beslid axially of cylinder I1 and may be fixed in any desired positionwithin the limits of slot I 8 by tightening screw 2 I. Plug I8 is chosenof a dielectric material such that cylinder l1, when acting as a waveguide filled with this dielectric material will no longer be belowcut-oil. but will freely transmit ultra high frequency of the operatingfrequency. Such a material may be Polystyrene," glass, etc.

Plug I8 carries at each end a resistor 22 and 23. These resistors may beformed in any suitable manner, such as by painting a coating of graphiteon the outer surface or plug I8 or by placing a suitable disc or slab ofresistive material such as carbon, in or on the ends of plug I8. Thepurpose of resistors 22 and 23 is to serve as terminating impedances forthe energy fed into or taken from the attenuator by way of wavedimensioned below cut-oil, the energy supplied to the attenuator throughwave guide I4 will tend to propagate along cylinder I1. However, thesection of cylinder I1, not containing dielectric plug I8, serves as awave guide dimensioned below cut-oil? and energy can no longer flowfreely through this latter section. In accordance with the well-knowntheory, discussed in the prior copending application, such a section ofwave guide serves as an attenuator, the amount of attenuation dependingupon the length of the restricted portion of wave guide.

In the present device, a second plug 28 of similar dielectric materialis also inserted in cylinder I1 and its position is preferably madeadjustable with respect to that of plug I8. Thus, plug 28 is fixed to asleeve 21 sliding on the outside of cylinder I1, as by means of a pin 28which freely passes through a slot 28 in cylinder I1. In Fig. 1, sleeve21 is shown as being rectangular in form and supplied with a rack 3ifixed to the underside thereof. Rack 3| cooperates with a pinion 32connected to an adjusting knob 33 journaled in a suitable bearing post34. In this manner, rotation of knob 33 serves to displace dielectricplug 28 along cylinder l1 and vary its separation from fixed plug I8.

As already discussed, cylinder I1 acts as a normal wave guide whenfilled with dielectric material, but as a wave guide below cut-off whensuch dielectric material is absent. Therefore, the adjutment of plug 28serves to effectively adjust the length of the section of cylinder I1which is acting as a wave guide below cut-oi'l'. Accordingly, the amountof high frequency energy fed through wave guide I4, which reaches plug28, may be varied by means of knob 83. The remaining energy isdissipated mainly in the walls of cylinder I1, and to a slight extent inthe terminating resistors 22 and 28.

Coupled to cylinder I1 is a transition section 3 composed of acylindrical portion 31 having a diameter suitable for the freepropagation of ultra high frequency energy therealong with airdielectric, and a section 38 which serves as a smooth transition betweenthe rectangular wave guide I8 and cylindrical section 31. For purposesof convenience, the diameter of section 31 may be chosen to be the sameas the maximum crosssectional dimension of wave guide I8. Dielectricplug 28 is provided with a smoothly tapering sec.- tion 39 which ispreferably chosen of a length equivalent to several wavelengths of theoperating frequency of the dielectric section 39. This portion of thedevice then acts to smoothly transfer the energy flowing within theportion of dielectric plug 28 within cylinder I1 to the wave guide I8through the transition section 38. Pref erably, a terminating resistor4|, similar to resistors 22 and 23, is placed on the left end of plug 28so that the impedance of the attenuator, when viewed from wave guide l8,will remain substantially constant and properly terminated, independentof the setting of plug 28.

If desired, a diaphragm, such as 42, may be inserted in wave guide I4and wave guide I8 to assist in matching the impedances of the source orload to that of the attenuator. Diaphragm 42 may be made adjustable inany well-known manner to provide an impedance matching adjustment.

A scale 43 may be mounted on the base II to cooperate with a pointer,fixed to the adjustable sleeve 21, whereby the desired attenuation maybe suitably selected.

It will thus be seen that I have provided a relatively simplyconstructable attenuator whose only movable part in the electricalportion of the system is a dielectric plug. Thus, the accurate machiningand complicated construction of the types of attenuator of the priorapplication are completely eliminated and replaced by a relativelysimply constructed and easily adjusted device.

Although, cylinder I1 has been described as having a circularcross-section, it is to be understood that this is so chosen forpurposes of convenience only, and that any suitable cross-section may beutilized, such as rectangular, elliptical, etc. This may be done in thepresent instance merely by correspondingly changing the cross-sectionsof plugs l8 and 28 and of sliding member 21. By making cylinder I1 arectangular cross-section, the necessity for a transition piece such as38 may be obviated.

Fig. 3 shows another form of attenuator accordin to the presentinvention. This modification is adapted to couple a concentrictransmission line to a wave guide, either of which may act as the inputor output terminal of the device. The concentric transmission line maybe connected to a concentric transmission line terminal post 45 in anysuitable manner. The inner conductor 48 of this terminal post extendsthrough an opening in the cylindrical casing 51 of the attenuator in theform of an antenna or probe 48. Also located within cylinder 41 is athick cylindrical plug 5|, which is adapted to slide axially of cylinder41. Plug 5| is preferably made of conducting material and is confined,solely, to axial translational movement along cylinder 41 by means of aslot 52 formed in cylinder 41 and a screw 53 passing freely through slot52 and securing plug 5| to a sleeve 54 sliding on the outside ofcylinder 41. Plug 5| is also provided with a slot 56 to avoid contactwith antenna 48 of terminal post 45.

Sleeve 54 is fixed to a rack 51 cooperating with a pinion 58 which maybe actuated by a knob, not shown, fastened to the shaft 59 or pinion 58,to iii lOVl-CIB an adjustment of the attenuation offered by the device.Cylinder 41 is connected to a wave guide 6| by a smooth transitionsection 82.

Plug is provided with an axial bore whose diameter is so chosen that theinterior of plug 5| may be considered to be a circular cross-sectionwave guide dimensioned below cut-off. Cylinder 41, on the other hand, isdimensioned to operate as a normal wave guide. It will be seen that byadjustment of shaft 59, the position of plug 5| relative to antennaprobe 48 may be changed, so that the effective length of the belowcut-off 'wave guide 5| to the right of antenna 48, may be suitablyadjusted. If energy is considered to be fed to the attenuator throughterminal post 45 and to be taken from the device through wave guide 6|,it will be seen that adjustment of plug 5| interposes an adjustablelength of cut-off wave guide in the path of energy flow, and therebyprovides adjustable attenuation for this energy. The left end ofcylinder 41 may stantially constant and properly-terminated, de-

spite the variable attenuation introduced by the device of theinvention.

It will be noted that, in the device of Fig. 5, the right end of waveguide 41' is left open. As

stated above with respect to Fig. 3, this has subbe closed by a.suitable cap 63 or may be left open, as desired, since the attenuationof. plug 5| to the left of antenna 48 may be made to provide enoughattenuation to prevent substantial leakage or radiation of energy fromcylinder 41 even if the left end were to be left open.

It is to be understood here, also, that the wave guides formed bycylinder 41 and plug 5| niay be any desired cross-section and that otherforms of energy input and output terminals may be utilized. For example,terminal post 45 may be replaced by a, suitable wave guide supplyingenergy within plug 5| in any suitable manner, or wave guide 6| may bereplaced by a concentric line terminal.

Fig. 5 shows another modification of the attenuator of the invention,and may be considered to represent a form of inversion of the deviceshown in Fig. 3. In this instance, the cylinder 41 is replaced by arectangular wave guide 41 and plug 5| is replaced by a pair ofconducting metallic members 5| and 5|", which act to restrict theeffective cross-section of this portion of the device with respect tothe flow of high frequency energy.

In the present instance, instead of adjusting plug 5| with respect tothe attenuator, the antenna probe 48 is made adjustable, in a mannersimilar to that shown in the preceding figures by means of a knob 64,pinion 65 and rack 66. Here, a self-contained source of high frequencyenergy, such as a suitable oscillator 61 or a suitable load may belocated directly upon movable sleeve 54' so that the coupling betweensource or load 61 and antenna 48 may be made short, as is desirable.

The theory of operation of the device of Fig. 5 will be seen to besubstantially identical with that of Fig. 3, since the length of thecut-off wave guide between the source and the load is made adjustable bythis apparatus; In order to present a substantially constant load to theoscillator or load 61 despite the variation of attenua tion offered bythe device of the invention, it is desirable to insert a terminatingimpedance, such as is generally indicated at 68, in the wave guide 6|.

As shown more clearly in Fig. I, terminating impedance 68 may comprise acarbon rod 1|,

stantially no effect on the operation of the system since theattenuation offered prevents appreciable energy radiation. g

If desired, the device of Fig. 5 could be made similar to that of F1 3by providing a cylindrical casing 41 with flxe plug 5| and a movableantenna 48 as in Fig. 5. The plugs 5| and 5|" of Figs. 5 and 6 may bemade as solid plugs of metal or may more simply be made of sheetmaterial having a thickness at least as great as the skin depth of thehigh frequency currents at the operating frequency. Also, in the deviceof Fig. 3, the plug 5| could be made fixed and the antenna 48 movable,as desired.

Figs. 8 and 9 show another form of attenuator according to the presentinvention. This modification is generally similar to that of Fig. 2, butdiscloses an inverted relationship of fixed plug l8 and movable plug 21of Fig. 2. Thus, in Fig. 8, plug 26 is maintained fixed and is providedwith tapered portion 89 for coupling the wave guide formed bycylindrical casing l1 and plug 26' with output wave guide IS. Aterminating resistor 68, which may be of the same form as that shown inFig. 7, is utilized here also, to terminate the portion of the system tothe left of the apparatus so that the impedance oifered by theattenuator will remain unchanged and properly matched when viewed fromthe left, despite a y variation, in the attenuation offered. Plug I8,corresponding to plug l8 of Fig. 2, is now made movable by anarrangement similar to that shown in any of the preceding figures, underthe control of knob 33. By adjustment of movable plug l8, the separationbetween dielectric plugs 26' and I8 may be varied. Since the portion ofcylindrical casing I1, between these two dielectric plugs, forms a waveguide dimensioned below cutoff, and since the portions of cylindricalcasing |1 containing the dielectric plugs 26' or I8 represent normalwave guide sections adapted tofreely transmit high frequency energy ofthe operating frequency, it will be seen that the present inventioninterposes an adjustable length of cut-oi! wave guide to the flow ofhigh frequency energy as in the preceding figures. Energy may besupplied to the attenuator or taken therefrom by means of a concentricline coupling 8| terminating in a probe 82 within a wave guide sectionl4 connected in T to the casing l1. A matching dia-' phragm 42 similarto that of Fig. 2, may be used.

It is to be understood that energy maybe supplied to wave guide M byconnecting other wave guides thereto in the manner shown in Fig. 2, ifdesired. Also, the energy couplingshown in Figs. 8 and 9 may be utilizedin the apparatus of any of the preceding figures, if desired.

Movable dielectric plug l8 carries suitable terminating resistors 22',23' at its ends, and plug 26' carries a terminating resistor 4| at itsend. Resistors 22 and 23' are chosen to have such resistance value thatthe wave guide I4 and the circuit coupled to it by coupling 8| will beproperly terminated for substantially all positions of dielectric plugl8, so that the impedance offered by the attenuator of the inventionwhen viewed through coupling 8! will not vary appreciably with change inthe attenuation value and will remain matched. Terminating resistor llassists in the loose coupling of the wave guide section formed by casingl1 and dielectric 26' with the cut-off wave guide formed by casing I1with air dielectric, The operation of the device of Figs. 8 and 9 issubstantially identical with that of the preceding figures.

It is to be noted that each of the attenuators of the present inventionis completely bilateral in character, that is, an energy source may beconnected to either end and an energy load or utilization device to theother end. Furthermore, in none of these modifications is the particularshape of wave guide critical so long as the functioning of the waveguide sections remains as described. The round or rectangular shapesillustrated have been utilized mainly for convenience of constructionand assembly, but may be replaced by any other types desired.

Although in Figs. 3 and the plugs 5|, 5| and 5|", restricting thecross-section of the wave guide, are preferably made of conductingmaterial, it is to be noted that they may also be made of dielectricmaterial, in which case the restricted wave guide section could be moreproperly termed a dielectric guide," since it would be formed by adielectric bounding medium for the space through which energy isconducted, rather than a metallic bounding medium as is the case withthe more usual wave guide.

It is to be noted that in each of the modifications of the presentinvention, the terminal wave guide sections may be replaced by suitableconcentric transmission line sections, either in the manner shown inFigs. 3 or 8, or in the manner shown in the preceding application SerialNo. 452,319. Furthermore, any of the concentric transmission lineterminals such as those shown in Figs. 3 or 8, may be replaced bysuitable wave guide terminals, where desired.

Accordingly, I have shown several forms of wave guide attenuator devicewhich are adapted to provide easily adjustable and attainable values ofattenuation for the flow of high frequency energy in wave guide orconcentric line systems.

As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An ultra high frequency attenuator, comprising a uniform wave guideadapted to freely transmit ultra high frequency energy of the operatingfrequency, means interposed in said wave guide to reduce the effectivecross-section thereof below the cut-off value corresponding to saidoperating frequency, ultra high frequency energy coupling meansconnected to said wave guide at one end thereof, further ultra highfrequency energy coupling means connected to said reduced cross-sectionportion of said wave guide, and means for adjusting the position of saidfurther coupling means with respect to said reduced section wave guideportion to vary the amount of attenuation introduced between said pairof coupling means.

2. An ultra high frequency attenuator as in claim 1, wherein saidlast-named means comprises means for adjusting said further couplingmeans along said wave guide.

3. An ultra high frequency attenuator as in claim 1, wherein saidlast-named means comprises means for adjusting said reduced section waveguide portion along said wave guide.

4. An ultra high frequency attenuator comprising a uniform wave guideadapted to freely transmit ultra high frequency energy of the operatingfrequency, means for modifying a portion of said wave guide to form awave guide section dimensioned below cut-off, whereby attenuation isinterposed to the flow of said energy through said wave guide, and meanscoupled to the electromagnetic field within said below-cutoff section,said modifying mean comprising means within said wave guide fordecreasing the effective cross-section thereof to form said below-cutoflsection and also including means for varying the position of saidcross-section-decreasing means along said guide relative to saidcoupling means to change the effective length of said below-cutoffsection to vary said attenuation.

5. An ultra high frequency attenuator comprising a uniform wave guideadapted to freely transmit ultra high frequency energy of the operatingfrequency, conductive means extending along and within said wave guidefor reducing the cross-section thereof through which said energy passesto a value below cut-off for said operating frequency, high frequencycoupling means connected at one end of said wave guide, high frequencyterminating means connected at the other end of said wave guide, furthercoupling means coupled to said wave guide within said conductive means,and means for varying the relative positions of said further couplingmeans and said conductive means, whereby an adjustable length ofbelow-cut-oif wave guide is interposed between said two coupling means.

6. An ultra high frequency attenuator comprising a uniform wave guideadapted to freely transmit ultra high frequency energy of the operatingfrequency, conductive means within said wave guide and extendingtherealong for reducing the cross-section of a section of said waveguide to a value below cut-off, ultra high frequency energy couplingmeans at one end of said wave guide, further ultra high frequency energycoupling means within said reduced cross-section, and means forlongitudinally varying the relative positions of said reducedcross-section section and said two coupling means for varying theattenuation between said two coupling means.

'7. Variable-amplitude ultra high frequency signal generator apparatus,comprising a source of ultra high frequency energy having an outputprobe, a uniform wave guide having a slot in one 55 face thereof forreceiving said probe, said wave guide having a cross-sectional areaadapted to freely transmit ultra high frequency energy of the frequencyof said source, conductive means within said wave guide at the locationof said probe and extending along said wave guide for for varying thelocation of said source along said slotted wall, whereby variablelengths of said below-cut-ofl' section are interposed between saidsource and said output coupling.

8. An ultra high frequency attenuator comprising a uniform wave guideadapted to freely transmit ultra high frequency energy of the operatingfrequency, conductive means within said wave guide and extendingtherealong for reducing the cross-section of a section of said waveguide to a, value below cut-off, ultra high frequency energy couplingmeans at one end of said wave guide, further ultra high frequency energycoupling means at said reduced cross-section, and means for varying thelength of said reduced cross-section section between said two couplingmeans for varying the attenuation between said two coupling means, saidlast-named means comprising means for moving said conductive meansrelative to said wave guide.

9. An ultra, high frequency attenuator comprising a uniform wave guideadapted to freely transmit ultra high frequency energy of the operatingfrequency, means movable within said wave guide for modifying a portionof said guide to form a wave guide section dimensioned below cut-off,whereby attenuation is interposed to the flow of said energy throughsaid wave guide, and coupling means extending within said movablemodifying means and longitudinally movable relatively thereto.

10. Variable-amplitude ultra high frequency signal generator apparatus,comprising a source of ultra high frequency energy having an outputprobe, a uniform wave guide having a slot in one face thereof forreceiving said probe, said wave guide havi a cross-sectional areaadapted to freely transmit ultra high frequency energy of the frequencyof said source, conductive means within said wave guide at the locationof said probe and extending along said wave guide for a predetermineddistance, whereby said wave guide cross-sectional area is reduced to avalue below cut-off, an output coupling connected to said wave guide atone end thereof, and means for varying the relative location of saidsource along said slotted wall with respect to said conductive 10 means,whereby variable length of said belowcut-ofi section are interposedbetweensaid source and said output coupling.

11. An ultra high frequency attenuator com prising a uniform wave guideadapted to freely transmit ultra high frequency energy of the operatingfrequency, conductive means within said wave guide and extendingtherealong for reducing the cross-section of a section of said waveguide to a value below cut-off, ultra high frequency energy couplingmeans at one end of said wave guide, further ultra high frequency energycoupling means within said reduced cross-section, and means for varyingthe length of said reduced cross-section section between said twocoupling means for varying the attenuation between said two couplingmeans and wherein said last-named means comprises means for moving saidconductive means relative to said wave guide.

12. An ultra high frequency device comprising an elongated hollowconductive member, conductive means extending along said member forreducing the cross-section thereof, high frequency energy coupling meansat a predetermined point of said member, further high frequency couplingmeans coupled to said conductive means, and means for longitudinallyadjusting said further coupling means and said conductive means relativeto one another.

13. An ultra high frequency attenuator comprising a uniform wav guideadapted to freely transmit ultra high frequency energy of the operatingfrequency, conductive means within said wave guide and extendingtherealong for reducing the cross-section of a section of said waveguide to a value below cut-off, ultra high frequency energy couplingmeans at one end of said wave guide, further ultra high frequency energycoupling means within said reduced cross-section, and means for varyingthe length of said reduced cross-section section between said twocoupling means, said last-named means comprising means for moving saidfurther coupling means relative to said wave guide and conductive means.

EDWARD L. GIN ZTON.

